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I am about finished welding the fusor parts together, and today I was able to test assemble the major part of my fusor.
The diametre of the sphere is 256mm internal, close to 10". Material thickness is 3mm or 1/8"

Finn Hammer's fusor 18-09-2017

It looks a bit flattish, but it is not. On the right side, you see the connection to the 3.5" diffusion pump, this connection widens out to mate with the 4" butterfly valve, which in turn mates to a 4" bend, which enters the sphere from the right. The bend contains halfmoon shaped baffels which overlap.
I felt I should run the diff. pump connection to the chamber keeping the cross section equal or bigger than the throat of the pump.
Another thing I am uncertain about is how fine controll I will have with the diff. pump running, and a 4" butterfly valve. I fear that the butterfly valve will let too much deuterium ply past it, even when it is only slightly open. To try to compensate for that, I am bypassing the butterfly valve with a 1" bellows valve which you see at the far right. I can close the butterfly valve completely and balance fusor pressure with the bellows valve. Or try to at least, we will see about that.
The main flanges are scrapped parts from a dairy supplyer, I turned them out and made conflat fitting on the mating surfaces, needless to say, I am anxious to see if they will hold a vacuum.
The viewport diametre is 2 1/2" and the feedtrough is a 30kV rated type, both conflat too. The arrangement of the feedtrough/viewport serves these purposes:
No parts from a melted grid will fall into any pump.
I will view the grid along its center axis, so I will get great photos in star mode
The viewport is pointed away from the operator
The high voltage connection is guarded inside the machine chassis, which is grounded, for maximum safety.

The 1" bellows bypass valve should work exactly as intended assuming you have an appropriate 'leak' type valve on the D2 input. I use a manual SS-bellows Varian 2.75" Conflat right angle valve for my gross pressure control between the chamber and the throat of my turbomolecular pump and it works great (takes a little fiddling to find the sweet spot during most runs).

Nick is absolutely correct. I have used only a 2.75 CF bellows valve to control the diff pump's conductance. (virtually closed off after evacuation to 5X10e-4 torr.) I barely cock open the valve and then open the needle valve in the D2 line and, as Nick notes, a good bit of fiddling is needed to start my fusor with about 6 microns of flowing D2 pressure. As time passes, I have no problem bumping this up to 10 or more microns to approach the mega mark near 40kv.

Once a perfect fusor is assembled to a high standard, getting it to work is all about fiddling and nothing else.....Fiddling with pressure, current, voltage to, at first, just achieve operation as the neutron counter starts to click. More and more fiddling to make it click faster and faster.

What Nick calls a bit of fiddliing turns out to be my preaching about experienced operator control and gaining knowledge of your particular system. Fiddling is part of the human-fusor feedback system that is a learned function on the part of the human mechanism to make a fusor perform.

Richard Hull

Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

A picture of the poor mans conflat in my fusor shell main flange seam.

Poor mans conflat, turned in dairy scrap stock.

Something that is coming up soon, is designing the gas delivery system.
Based on this discussion:viewtopic.php?f=24&t=2570&p=12080&hilit ... lve#p12080
I have setteled on using a mass flow controller, so that I can deliver 0-10 sccm of deuterium into the shell.
I assume that with for example 5sccm of deuterium flowing, I should be able to run the fusor for 3 hours per liter deuterium 1000cc/5ccm=200m =>~3 hours, so a 25 liter bottle should last 75 hours, this number seems very large I must have miscalculated.....
The reduction valve is a Matheson 3320, and the flowcontroller is a refurbished MKS M100B01311CS1BV

I read that people use very long capillary tubes and/or holes in the micron range to choke the deuterium supply, but can I rely on this system to work, with a 0-5V input.
I have a problem going through the calculations on page 62-65 mainly because the table on page 63 assumes that the valve delivers gas into atmospheric pressure, but the fusor sucks at ~10micron.
The manual for the Controller can be found here:http://www.mksinst.com/docs/r/m100b-m10mbman.pdf

From your picture above it appears there is some pitting in your weld on the inside of your chamber. I’d imagine this will limit the ultimate pressure you can achieve, but I do not have any practical experience to say what that limit might be. Fusors do not require much of a vacuum in the scheme of things so it probably doesn't matter.

Can you post a couple clearer pictures of the inside chamber welds as a data point? I’ll be keenly watching to see your results when you have the diffusion pump connected.

When I built fusor IV, I welded the rings on the hemisphere and put in the vacuum port and Baratron port only. I pumped the system down and checked for leaks. I had a couple of minor leaks around my welds at the rings, which I fixed.

It is only after checking out the basic chamber and large weldments that I starting adding ports one by one and pulling down to a vacuum. In this manner I could be fairly sure that any leaks once the system went together were leaks in the vacuum line and system plumbing outside of the fusor.

Currently, what leaks I do have, which are minor, are indeed in the various connections.

Richard Hull

Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Good procedure, I should have thought of doing something like that, and not rush things.

Bruce,

Not so bad an idea to take photos.
I wish it all looked like this:

Or even like this:

Even this one looks acceptable, I see only surface slag:

This shift has a big black spot, I think it is just a surface slag, but notice the micro-pores to the left of that spot. It is going to get very interesting to try to pull this chamber to a high vacuum.

But here I start to worry: It looks like craters that could go deep. and maby penetrate to the outside.

This is my first attempt at a vacuum vessel, and I am just hoping for the best. We will see soon enough.

I took some pictures off a 4" Conflat flange, produced by Kurt Lesker. The uniformity of the welding pattern reveals that this is an automated weld out of a welding robot, nevertheless it displays some of the same flaws that tarnished my own work:

However, things tend to get out of proportion when viewed trough a macro lens, that's kind of the purpose I guess, like this little critter. In real life only 6mm long (1/4") but viewed with the same macro, it becomes a monster:

To be accepted as a customer by Sigma Aldrich is not a trivial task, but finally I passed through the eye of the needle, and the bottle arrived yesterday, I cannot tell you how happy I am.

A nice 25L bottle of Deuterium

Together with this reduction valve:

The gas delivery system that I am planning will consist of a mass flow controller, and for that purpose, I have aquired this classy unit, refurbished by MKS, so as good as new, I assume:

MKS Model M100B01311CS1BV 10 SCCM N2 Mass Flow Controller Refurbished

Initially, I had some bad reservations about using a flow controller due to a misconception of mine: I assumed that since D2 is less dense than N2, then the valve would pass much more D2, but this is not really the case.
Reading the manual revealed some great news: The controller works by measuring the flow of gas by a method that relies on both the density of the gas, as well as the specific heat of the gas. The product of these two constants multiplied goes into the formula for the delivery of the gas, in the form of the conversion factor, and it so turns out that this factor is the same for N2 and D2.
N2 has specific heat: 0.2485 and density is 1.2500 multiplied = 0.3106
D2 has specific heat: 1.7720 and density is 0.1799 multiplied = 0,3187, or close enough for a conversion factor of 1.
Another great feature of the flow controller is the ability to controll a pressure:

The normal way of operation is to choose a set point between 0-5V and this will in this case correspond to 0-10sccm of D2 flow.
But there is another input, called the optional input. By feeding the output from my 50micron full scale Baratron into that input I get this functionality:
By setting the flow controller set point to the baratron output at the desired pressure, the flow controller will adjust the flow to maintain that pressure.
An example:
Scaling the 0-10V output of the baratron to the 0-5V input of the flow controller, then 5-50micron on the baratron will produce an output signal from 0.5 - 5V, with 0.1V/micron. So in the case that I want to maintain a pressure of 10 microns, the set point voltage on the flow controller should be 0.5 + (10*0,1) = 1.5V
How this is going to work out in idle mode is probably straight forward, but when the corona kicks in, things may look quite different, time will tell.

So this was a short account of how my work and understanding of things involved is coming along.

Congratulations! I understand - I had to set up a "business" and do the paperwork with the State in order to get mine to work (Tax number and all that.) Cost me both trouble (a number of years dealing with paper work but on the plus side, I did work with a company on an SBIR.) Good work and I know you will soon be going fusion.